1. Field of the invention
The present invention relates to a sensor probe for use in board inspection, more particularly to a sensor probe for inspecting a circuit board having a microscopic wiring pattern, and a manufacturing method thereof.
2. Prior Art
For inspecting a circuit board having a microscopic pattern, an inspection signal has hitherto been applied to a number of pins which had been pressed to respective terminals of a board as an object to be inspected. In this method, a rubber sheet is provided on the board in order to reduce the load which is caused from the press of the number of pins and applied to the board. This often causes a problem of loose connection due to the rubber sheet interposed between the pins and the board.
To solve this problem, for example, in Japanese Patent Laid-Open Publication No.
Hei 9-264919, applied for by the present applicants, there is provided a method for inspecting a defect of a board in such a way that a signal is picked up on a non-contact basis by use of a probe (electrode) having a size lager than a width of a wiring pattern as an inspecting object.
Japanese Patent Laid-Open Publication No. Hei 8-278342 also discloses electrodes (stimulator) 11A and 11B for generating an inspection signal toward a board and a plurality of electrodes 12A, 12B, 12C, . . . for receiving a radiation signal from the board, as shown in FIG. 1.
The common idea among Japanese Patent Laid-Open Publications Nos. Hei 9-264919 and Hei 8-278342 is to inspect a plurality of pattern lines by an electrode having a size as large as that capable of covering the pattern lines in a lump and also on a non-contact basis.
Sensor probes which are used in Japanese Patent Laid-Open Publications Nos. Hei 9-264919 and Hei 8-278342 are intended to inspect a circuit pattern having a pitch and size as large as those of a typical printed circuit board, and their integration degree is in low level. Therefore, subject to forming their sensor electrode portion by means of a particular process, such as machining and simplified etching, sufficient accuracy would be obtained.
In those sensor probes of the prior art, the electrode having the size as large as that capable of covering a plurality of pattern lines is used to eliminate the need for high alignment accuracy. Thus, these sensor probes can neither inspect a particular size of circuit pattern, for example approximately 50 xcexcm or not greater than 50 xcexcm, with high resolution, nor apply to a circuit board in which the wiring pattern branches along its way. In addition, it is impossible to inspect a defective status in which the pattern is not completely broken and is partly chipped away.
It is an object of the present invention to provide a method of manufacturing a microscopic board sensor probe through a semiconductor process, and further to provide a circuit board sensor probe having a structure suitable for microscropic size.
According to one aspect of the present invention proposed to achieve the object described above, there is provided a manufacturing method of a sensor probe for use for board inspection as follows, in a manufacturing method of a sensor probe for use in board inspection, the sensor probe comprising layers which include an electrode layer, a lead wire layer and a bridge layer, the layers being laminated on a base in formed of a flat plate composed of either of silicon and silicon oxide, the electrode layer being comprised of a set of sensor electrodes, the lead wire layer being comprised of a set of lead wires for transferring a signal to outside, the bridge layer coupling between the electrode layer and the lead wire layer, the method comprising steps of: forming the lead wire layer by making a set of lead wires prepared by means of forming a film from a predetermined conductive material on the base in accordance with a first mask pattern; forming the bridge layer by making each of the bridge wires prepared by means of growing a film formed from a predetermined conductive material in the direction perpendicular to the base, the bridge wires being respectively connected to respective lead wires of the lead layer and being extended in the direction perpendicular to the base; and forming the electrode layer by making a set of sensor electrodes prepared by means of forming a film from a predetermined conductive material in accordance with a second mask pattern, the plurality of sensor electrodes being respectively extended in the horizontal direction and having a predetermined area.
In this method, each layer as sensor elements is substantially formed by using a semiconductor process so that it may meet the requirements of making sensor elements of microscopic size or optional requirements on the figuration of the electrode.
According to another aspect of the present invention, there is provided a sensor probe for use in board inspection as follows, in a sensor probe for use in board inspection, wherein layers which include an electrode layer, a lead wire layer and a bridge layer are laminated on a base in formed of a flat plate composed of either of silicon and silicon oxide, the electrode layer being comprised of a set of sensor electrodes, the lead wire layer being comprised of a set of lead wires for transferring a signal externally, the bridge layer coupling between the electrode layer and the lead wire layer, the sensor probe comprising: the lead wire layer including a plurality of lead wires which are formed on the base and are connected to an outside pad; the bridge layer including a plurality of bridge wires which are respectively connected to respective lead wires of the lead layer and are extended in the direction perpendicular to the base; and the electrode layer including a set of sensor electrodes which respectively extend in the horizontal direction from respective lead wires and have a predetermined area. In respective sensor elements, the electrodes and the bridge wires are arranged in the vertical direction so that the entire size of the probe may be maintained even when number of sensor elements are arranged in the direction along a surface of the base. This results in a high degree of integration.
According to a preferred embodiment of the present invention, the electrode layer is formed in the surface direction by means of forming a film from either of aluminum and copper. Thus, adequate electrode functioning may be assured due to the resulting area.
According to another preferred embodiment of the present invention, the bridge layer is formed in the vertical direction by means of growing either of aluminum and copper so that the bridge wires may be thinned.
According to other preferred embodiment of the present invention, the lead wire layer is formed in the surface direction by means of forming a film from either of aluminum and copper or growing either of aluminum and copper.
When making the probe microscopic, problems, such as a cross talk between each sensor or noise from other sensor outputs, occur. Thereat, according to still other preferable embodiment of the present invention, a cross-sectional area of each bridge wire is set in smaller than an area of each electrode. Then an electrical shield layer, which is provided between the electrode layer and the lead wire layer making the electrical shield layer not to contact each bridge wire, is formed by means of forming a film from a predetermined conductive material in accordance with a third mask pattern, the electrical shield layer being extended in the direction along the flat surface of the base.
When such a shield is made of metals, insulation would be a key factor. Thus, according to yet other preferable embodiment of the present invention, a first insulation layer is provided between the electrode layer and the lead layer, and each bridge wire of the bridge layer is formed penetrating the first insulation layer.
In the same objective described above, according to further preferable embodiment of the present invention, a second insulation layer is provided between the electrode layer and the shield layer, and a third insulation layer is provided between the shield layer and the lead layer, wherein the second insulation layer and the third insulation layer are coupled each other in the vicinity of respective bridge wires. This enables each bridge wire to be assured not to electrically connect to any of the shield layers.
According to still further preferable embodiment of the present invention, each electrode of the electrode layer is provided horizontally on the flat surface of the circuit board as an inspecting object.
A pad is necessary for outputting an external signal due to the microscropic-sized lead wires. Thereat, according to yet further preferable embodiment of the present invention, each lead wire of the lead wires is connected to respective pads.
According to the remaining embodiment of the present invention, the predetermined conductive material is either of aluminum and copper.
The microscopic size results in weakened output from the sensor element. Thus it is desirable to execute signal conditioning in the proximity of the sensor. Thereat, according to the remaining embodiment of the present invention, a signal conditioning circuit is formed in the base.